Just took a quick listen to CYYZ Arrivals and both controller and aircraft can be heard. Could be they were using a frequency
not covered by LiveATC for the arrivals at the time you were listening. If you have a scanner and live close enough to the
airport you could listen to the arrival frequencies shown in LiveATC and see if you hear the aircraft on your scanner. You may
not hear the controller side, all depends on your location. Since you heard the controller side on LiveATC, doesn't seem likely the problem is with your computer.